A transparent conductive film exhibits high conductivity and high transmittance within a visible light range. For this reason, the transparent conductive film is used as an electrode for a solar cell, a liquid crystal display (LCD) device, an organic electroluminescent (EL) display, an inorganic EL display, a touch panel, and various light sensitive elements. In addition, the transparent conductive film is widely used in various fields, such as a solar reflective film and an anti-static protective film for vehicle windows or buildings.
For a transparent conductive film applied to a display device, particularly an organic EL display, low specific resistance and high flatness are required due to characteristics of the device. In particular, high flatness of the transparent conductive film is much more required than low specific resistance of the transparent conductive film due to a small thickness of an organic light emission layer thereof. For a transparent conductive film applied to a solar cell, on the other hand, efficiency of converting solar light to electricity is most important. For this reason, low specific resistance as well as high light transmittance of the transparent conductive film is requisite due to characteristics of the application field.
A transparent conductive film which has been industrially widely used is an indium oxide (In2O3) thin film. In particular, indium tin oxide (ITO), which is indium oxide including tin as a dopant, has been widely used since it is possible to easily manufacture a transparent conductive film exhibiting low resistance using the indium tin oxide (ITO).
The indium oxide (In2O3) transparent conductive film is generally manufactured using vacuum deposition methods, such as a sputtering method, a metal organic chemical vapor deposition (MOCVD) method, and an ion plasma method, and an aerosol spray pyrolysis method.
The sputtering method is effective in a case in which it is necessary to accurately control formation of a film using a material exhibiting low vapor pressure or the thickness of the film. Since it is very easy and convenient to manipulate the sputtering method, the sputtering method is industrially widely used. In the sputtering method, however, sputtering defects may be directly generated at a p type optical absorption layer located at the lower part of the film. In addition, it is difficult to use the vacuum deposition methods in producing large-sized products due to economical and technical problems caused when the size of a vacuum furnace is increased to a large scale. In the aerosol spray pyrolysis method, on the other hand, the thickness of the thin film is not uniform and it is difficult to control the size of coating particles with the result that transparency of products is lowered.
For this reason, there has been proposed a coating method for applying an application liquid to form a transparent conductive film, which is industrially applicable since it is easy to control the size of coating particles, formation of a thin film, and the thickness of the thin film at a low cost and it is possible to perform face-to-face coating.
During heat treatment of the application liquid, however, a lower layer may be denaturalized due to high-temperature heat treatment. In a case in which low-temperature heat treatment is carried out to prevent such a problem, arrangement of crystal particles in the thin film is not perfect with the result that polycrystalline growth may be caused. In addition, a final thin film exhibits a surface resistance of hundreds of ohm. That is, physical properties of the thin film are lowered as compared with the characteristics of the conventional transparent conductive film with the result that it is difficult to industrially apply the coating method.
Therefore, there is a high necessity for a method of manufacturing a transparent conductive film which can be carried out with lower cost than a conventional process of manufacturing a transparent conductive film, provide high material efficiency, and manufacture a transparent conductive film exhibiting physical properties equivalent to those of a conventional transparent conductive film.